﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Baitap09
{
    public abstract class Talk
    {
        public abstract void speak();
        public virtual void goobye(){
            Console.WriteLine("Says goodbye!");
        }
    }
    public class SayHello: Talk{
        public override void speak(){
            Console.WriteLine("Says Hello!");
        }
    }
    class Program{
        static void Main()
        {
            SayHello hello = new SayHello();
            hello.speak();
            hello.goobye();
        }
    }
}
